1. Field of the Invention
This invention relates generally to electronic identification and recognition systems and more specifically to such systems wherein it is not necessary to make physical contact between the identification card and the recognition apparatus.
2. Description of the Prior Art
There are various electronic identification and recognition systems wherein the identifying device is portable. Sometimes the identifying device is referred to as a "card," "tag," "key," or the like. The recognition station or reader station is prepared to recognize identifying devices of predetermined characteristics when such identifying device is brought within the proximity of the reader station. Inductive coupling takes place between the two devices when they are proximate to one another and it is not necessary to bring the device into physical contact. Though, the identifying device may contain a battery, it usually receives its energy from the reader station.
Uses for such systems may include identification of persons having identifying devices in their possession. For example, the identifying device may take the shape of a credit card and having an electronic circuit embedded therein for radiating signals of identifying intelligence. An individual possessing the card may position it adjacent a door that the individual desires to enter. A recognition device may be arranged to control the door latch and if it recognizes radiated signals of certain predetermined intelligence, the door latch responds to the reader when the individual places the "card" proximate to the reader. Other uses for such systems include having the identifier in the form of a tag attached to a vehicle to be identified. As the vehicle passes a certain location, it's identification is recognized and recorded. Also, in production lines, garments or other items may carry identifying tags so that they can be appropriately processed as they are recognized along various points in the production processes.
The prior art includes various patents and patent applications by the present inventor. The patents include U.S. Pat. No. 3,752,960 for "lectronic Identification and Recognition System," issued Aug. 14, 1973; U.S. Pat. No. 3,816,708 for "Electronic Recognition and Identification System," issued June 11, 1974; U.S. Pat. No. 3,816,709 for "Electronic Identification and Recognition System," issued June 11, 1974; U.S. Pat. No. 4,142,674 for "Recognition and Identification Key Having Adaptable Resonant Frequency and Methods of Adapting Same," issued Mar. 6, 1979; U.S. Pat. No. 4,223,830 for "Identification System," issued Sept. 23, 1980; U.S. Pat. No 4,236,068 for "Personal Identification and Signaling System," issued Nov. 25, 1980; U.S. Pat. No. 4,384,288 for "Portable Radio Frequency Emitting Identifier," issued May 17, 1983; and U.S. Pat. No. 4,388,524 for "Electronic Identification and Recognition with Code Changeable Reactants," issued June 14, 1983; U.S. Pat. No. 4,459,474 for "Identification System with Separation and Direction Capability and Improved Noise Rejection," filed on May 18, 1981; U.S. Pat. No. 4,473,825 for "Electronic Identification System with Power Input-Output Interlock and Increase Capabilities," filed on Mar. 5, 1982; U.S. Pat. No. 4,546,241 for "Identification System with Synchronous Modulation of Return Signal," filed on Dec. 10, 1982; U.S. Pat. No. 4,580,041 for "Electronic Proximity Identification System With Simplified Low Power Identifier," issued Apr. 1, 1986; and U.S. Pat. No. 4,600,829 for "Electronic Proximity Identification and Recognition System with Isolated Two-Way Coupling," issued on July 15, 1986.
Also, the prior art includes U.S. Pat. No. 3,732,465 for "Electronic Sensing and Actuator System," issued May 8, 1973 to Ronald S. Palmer and Charles A. Walton; U.S. Pat. No. 3,842,246 for "Recognition and Identification System with Noise Rejection Capabilities," by Robert D. Kohler, David P. Sidlauskas and Charles A. Walton, issued May 18, 1976; U.S. Pat. No. 3,958,105 for "Electronic Recognition and Identification System for Identifying Several Master Keys," issued May 18, 1976 to David P. Sidlauskas; and U.S. Pat. No. 3,970,824 for "Electronic Recognition and Identification System for Identifying a Family of Codes," by Charles A. Walton, Robert D. Kohler, and David P. Sidlauskas, issued July 20, 1976.
In the electronic portable recognition and identifier systems of the prior art, there are two directions of communications between the reader and the identifier devices. The reader (recognition section), which is typically stationary, must send an interrogation signal and/or power to the identifier device (e.g., card, tag, key), which is typically portable. In response, the identifier device sends a coded signal bearing intelligence about its identification to the reader. Means must be provided so that two directions of communication and power do not interfere to the extent of inhibiting the desired transfers. In the general class of electronic portable identification and recognition systems, inductive coupling is used between the reader and the identifier, although electric field dipole antenna coupling can also be used. A further characteristic is that often both power and data are transmitted over the same inductively coupled coils. In some of the reference prior art, noninterference between the two paths of the reader and identifier is achieved by engineering principles such as time separation, or differing frequencies, or by modulation of the electromagnetic power field and detection of such modulation in the radiated reader field. A disadvantage of time separation is the increase in total transaction time. A disadvantage of differing frequencies is that the coil of the portable identifier cannot be tuned simultaneously to two different frequencies. Such inability to tune, makes one direction inefficient. A disadvantage of power field modulation is that power losses occur in the identifier when the identifier modulates the power field. Another disadvantage of power field modulation is that the recognition antenna cannot be operated at peak voltage, but must be operated at frequencies on either side of the resonance curve in order for the changes in amplitude to be detectable.